Hearing Partial Discharge Inside Sealed Switchgear

PDPartial Discharge

Airborne ultrasonic inspection picked up the high-frequency signature of partial discharge inside energized medium-voltage switchgear — an invisible, inaudible fault developing toward flashover — flagged for correction at the next planned outage.

Elevated — Scheduled For Next Outage

Client: Ridgeway Industrial (name changed for confidentiality)

The challenge

Partial discharge inside medium-voltage switchgear is one of the most dangerous faults to catch — because it hides. It can develop inside sealed, energized equipment with no visible heat signature for an infrared camera to see and nothing audible to a person standing beside it. Left alone, it erodes insulation until it escalates to a flashover: a catastrophic, potentially injurious failure.

Our approach

We performed an airborne ultrasonic inspection of the energized switchgear. Partial discharge emits a distinctive high-frequency acoustic signature — well above human hearing — that ultrasonic instruments are built to detect. Scanning the gear while it was live and under normal load let us listen for that signature without any interruption to operations.

• Non-invasive inspection performed on energized equipment — no shutdown required to detect
• High-frequency ultrasonic signature captured and assessed for severity
• Finding documented and prioritized against the facility's outage schedule

What we found

The inspection picked up the unmistakable signature of partial discharge inside the sealed, energized switchgear — a fault actively developing toward flashover, invisible to infrared and inaudible to the naked ear. Severity assessed as elevated: serious, but not yet immediate.

Infrared + Ultrasonic Thermography sees heat; ultrasonic hears the faults that never get hot. Together they cover failure modes neither catches alone — which is why PD inside sealed gear needs an ear, not just an eye.

The outcome

Because the discharge was found early, it didn't become an emergency. The fault was flagged for correction at the next planned outage — letting the facility repair it on their schedule, safely and on budget, instead of reacting to a flashover.

Hear the faults infrared can't see

Partial discharge develops silently inside sealed gear. Ultrasonic inspection finds it while it's still a scheduled repair.